Question

Class Design – IntList (A.k.a. ArrayList (v0.0))

Let’s build a useful class that wraps up an array of integers. This class will store two data items; one an array of integers, and the other a counter to track the number of actual elements in the list. Start by defining a new class called IntList and copying the main driver code included below or in IntList.java. Then, add each of the following functions and data items indicated in the member sections. The IntList.java file shows an example of a char list, be sure to change it to a list of integers in order to complete the assignment.

Data Members

• Declare an integer array called “data”
  • Make this private and able to store up to 100 integers
• Declare an integer called numElements
  • Make this private, and set it to zero.

Method Members

• public void add(int n) {
  • this should add the value n to our array and add one to num_elements
• public String toString() {
  • String retVal=””;
    • In a loop, append all the elements in our data array to this string, separated by a comma
  • return retVal;
• Copy the main driver below and run it to test your IntList so far
  • Do you see output for each integer added to your list?
  • “95 100 58 ” //for example
• Next, uncomment each of the commented lines in main and build the corresponding function
  • Build a function to sum the integer elements stored in your IntList.
  • public int sum() {
    • This function takes no parameters; uses the class-level data[] array instead
• Since the next function is similar to sum(), copy and paste sum() and rename it to “indexOf”
  • Also, add an input parameter to the method signature called target, which is an int that we’re looking for in our list of integers.
  • public int indexOf(int target) {
    • takes a target parameter that we’re looking for
    • This returns -1 if not found

public static void main(String[] args) { 
    IntList a = new IntList();
    a.add(95); a.add(100); a.add(58);
    System.out.println(a.toString() );
    //System.out.println(a.sum() );
    //System.out.println(a.indexOf(100)); //uncomment these to work on next
    //System.out.println(a.indexOf(20));
    //System.out.println(a.save() );
}

Answer 1

 class IntList 
 {
    //Declare a private integer array called “data ” with size 100
     private int[] data=new int[100];
     //Declare an integer called numElements
     private int numElements=0;
     //add() method add the value n to array data and add one to num_elements
     public void add(int n)
     {
         //add the value n to array data
        data[numElements]=n;
        //add one to num_elements
        numElements++;

     }
     //In a loop, append all the elements in our data array to this string, separated by a comma
     public String toString() {
         //Declaring loop variable i
        int i;
        //Declaring a string retVal to store the output string
        String retVal="";
        //Loop to access elements in array data
        for(i=0;i<numElements;i++)
        //Concatinating array elements to string
        retVal+=" "+data[i];
        //Return resulting string
        return retVal;
     }
     //function to sum the integer elements stored in IntList
     public int sum() 
     {
         //Declaring integer variable sumElements to store sum of array elements
         int sumElements=0;
         //Declaring loop variable i
         int i=0;
         //Loop to access elements in array data
         while(i<numElements)
         {
             //Add each element to sumElements
             sumElements+=data[i];
             //Incrementing loop variable
             i++;
         }
         //Returning sum of array elements
         return sumElements;
     }
     public int indexOf(int target) 
     {
         //Declaring integer variable to store index of target variable
        int index=-1;
        //Declaring loop variable i
        int i=0;
        //Loop to access elements in array data
        while(i<=numElements)
        {
            //Checking if array element is equal to value of target if yes set index=i and break from loop 
            if(data[i]==target)
            {
               index=i;
                break;
            }
             //Incrementing loop variable 
            i++;
        }
        //Return index value
        return index;
     }
public static void main(String[] args)
 { 
    IntList a = new IntList();
    a.add(95); a.add(100); a.add(58);
    System.out.println(a.toString() );
    System.out.println(a.sum() );
    System.out.println(a.indexOf(100)); //uncomment these to work on next
    System.out.println(a.indexOf(20));
    //System.out.println(a.save() );
 }
}

Sample Output

Since there were no instructions for save() method it is not implemented